Third generation (3G) mobile systems, such as, for instance, universal mobile telecommunication systems (UMTS) standardized within the third generation partnership project (3GPP) have been based on wideband code division multiple access (WCDMA) radio access technology. Today, 3G systems are being deployed on a broad scale all around the world. After enhancing this technology by introducing high-speed downlink packet access (HSDPA) and an enhanced uplink, also referred to as high-speed uplink packet access (HSUPA), the next major step in evolution of the UMTS standard has brought the combination of orthogonal frequency division multiplexing (OFDM) for the downlink and single carrier frequency division multiplexing access (SC-FDMA) for the uplink. This system has been named long term evolution (LTE) since it has been intended to cope with future technology evolutions.
The LTE system represents efficient packet based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. The detailed system requirements are given in 3GPP TR 25.913, “Requirements for evolved UTRA (E-UTRA) and evolved UTRAN (E-UTRAN),” v8.0.0, January 2009, (available at http://www.3gpp.org/ and incorporated herein by reference). The Downlink will support data modulation schemes QPSK, 16QAM, and 64QAM and the Uplink will support BPSK, QPSK, 8PSK and 16QAM. LTE's network access is to be extremely flexible, using a number of defined channel bandwidths between 1.25 and 20 MHz, contrasted with UMTS terrestrial radio access (UTRA) fixed 5 MHz channels. Spectral efficiency is increased by up to four-fold compared with UTRA, and improvements in architecture and signaling reduce round-trip latency. Multiple Input/Multiple Output (MIMO) antenna technology should enable 10 times as many users per cell as 3GPP's original WCDMA radio access technology. To suit as many frequency band allocation arrangements as possible, both paired (frequency division duplex FDD) and unpaired (time division duplex TDD) band operation is supported. LTE can co-exist with earlier 3GPP radio technologies, even in adjacent channels, and calls can be handed over to and from all 3GPP's previous radio access technologies.
FIG. 1 illustrates structure of a component carrier in LTE Release 8. The downlink component carrier of the 3GPP LTE Release 8 is sub-divided in the time-frequency domain in so-called sub-frames each of which is divided into two downlink slots 120 corresponding to a time period Tslot. The first downlink slot comprises a control channel region within the first OFDM symbol(s). Each sub-frame consists of a given number of OFDM symbols in the time domain, each OFDM symbol spanning over the entire bandwidth of the component carrier. The smallest unit of resources that can be assigned by a scheduler is a resource block 130 also called physical resource block (PRB). A PRB 130 is defined as NsymbDL consecutive OFDM symbols in the time domain and NscRB consecutive sub-carriers in the frequency domain. In practice, the downlink resources are assigned in resource block pairs. A resource block pair consists of two resource blocks. It spans NscRB consecutive sub-carriers in the frequency domain and the entire 2·NsymbDL modulation symbols of the sub-frame in the time domain. NsymbDL may be either 6 or 7 resulting in either 12 or 14 OFDM symbols in total. Consequently, a physical resource block 130 consists of NsymbDL×NscRB resource elements 140 corresponding to one slot in the time domain and 180 kHz in the frequency domain (further details on the downlink resource grid can be found, for example, in 3GPP TS 36.211, “Evolved universal terrestrial radio access (E-UTR); physical channels and modulations (Release 8)”, version 8.9.0, December 2009, Section 6.2, available at http://www.3gpp.org. which is incorporated herein by reference).
The number of physical resource blocks NRBDL in downlink depends on the downlink transmission bandwidth configured in the cell and is at present defined in LTE as being from the interval of 6 to 110 PRBs.
The data are mapped onto physical resource blocks by means of pairs of virtual resource blocks. A pair of virtual resource blocks is mapped onto a pair of physical resource blocks. The following two types of virtual resource blocks are defined according to their mapping on the physical resource blocks in LTE downlink:                Localised Virtual Resource Block (LVRB)        Distributed Virtual Resource Block (DVRB)        
In the localised transmission mode using the localised VRBs, the eNB has full control which and how many resource blocks are used, and should use this control usually to pick resource blocks that result in a large spectral efficiency. In most mobile communication systems, this results in adjacent physical resource blocks or multiple clusters of adjacent physical resource blocks for the transmission to a single user equipment, because the radio channel is coherent in the frequency domain, implying that if one physical resource block offers a large spectral efficiency, then it is very likely that an adjacent physical resource block offers a similarly large spectral efficiency. In the distributed transmission mode using the distributed VRBs, the physical resource blocks carrying data for the same UE are distributed across the frequency band in order to hit at least some physical resource blocks that offer a sufficiently large spectral efficiency, thereby obtaining frequency diversity.
In 3GPP LTE Release 8 there is only one component carrier in uplink and downlink. Downlink control signaling is basically carried by the following three physical channels:                Physical control format indicator channel (PCFICH) for indicating the number of OFDM symbols used for control signaling in a sub-frame (i.e. the size of the control channel region);        Physical hybrid ARQ indicator channel (PHICH) for carrying the downlink ACK/NACK associated with uplink data transmission; and        Physical downlink control channel (PDCCH) for carrying downlink scheduling assignments and uplink scheduling assignments.        
The PCFICH is sent from a known position within the control signaling region of a downlink sub-frame using a known pre-defined modulation and coding scheme. The user equipment decodes the PCFICH in order to obtain information about a size of the control signaling region in a sub-frame, for instance, the number of OFDM symbols. If the user equipment (UE) is unable to decode the PCFICH or if it obtains an erroneous PCFICH value, it will not be able to correctly decode the L1/L2 control signaling (PDCCH) comprised in the control signaling region, which may result in losing all resource assignments contained therein.
The PDCCH carries control information, such as, for instance, scheduling grants for allocating resources for downlink or uplink data transmission. A physical control channel is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). Each CCE corresponds to a set of resource elements grouped to so-called resource element groups (REG). A control channel element typically corresponds to 9 resource element groups. A scheduling grant on PDCCH is defined based on control channel elements (CCE). Resource element groups are used for defining the mapping of control channels to resource elements. Each REG consists of four consecutive resource elements excluding reference signals within the same OFDM symbol. REGs exist in the first one to four OFDM symbols within one sub-frame. The PDCCH for the user equipment is transmitted on the first of either one, two or three OFDM symbols according to PCFICH within a sub-frame.
Another logical unit used in mapping of data onto physical resources in 3GPP LTE Release 8 (and later releases) is a resource block group (RBG). A resource block group is a set of consecutive (in frequency) physical resource blocks. The concept of RBG provides a possibility of addressing particular RBGs for the purpose of indicating a position of resources allocated for a receiving node (e.g. UE), in order to minimise the overhead for such an indication, thereby decreasing the control overhead to data ratio for a transmission. The size of RBG is currently specified to be 1, 2, 3, or 4, depending on the system bandwidth, in particular, on NRBDL. Further details of RBG mapping for PDCCH in LTE Release 8 may be found in 3GPP TS 36.213 “Evolved Universal terrestrial Radio Access (E-UTRA); Physical layer procedures”, v8.8.0, September 2009, Section 7.1.6.1, freely available at http://www.3gpp.org/ and incorporated herein by reference.
Physical downlink shared channel (PDSCH) is used to transport user data. PDSCH is mapped to the remaining OFDM symbols within one sub-frame after PDCCH. The PDSCH resources allocated for one UE are in the units of resource block for each sub-frame.
FIG. 2 shows an exemplary mapping of PDCCH and PDSCH within a sub-frame. The first two OFDM symbols form a control channel region (PDCCH region) and are used for L1/L2 control signaling. The remaining twelve OFDM symbols form data channel region (PDSCH region) and are used for data. Within a resource block pairs of all sub-frames, cell-specific reference signals, so-called common reference signals (CRS), are transmitted on one or several antenna ports 0 to 3. In the example of FIG. 2, the CRS are transmitted from two antenna ports: R0 and R1. Moreover, the sub-frame also includes UE-specific reference signals, so-called demodulation reference signals (DM-RS) used by the user equipment for demodulating the PDSCH. The DM-RS are only transmitted within the resource blocks in which the PDSCH is allocated for a certain user equipment. In order to support multiple input/multiple output (MIMO) with DM-RS, four DM-RS layers are defined meaning that at most, MIMO of four layers is supported. In this example, in FIG. 2, DM-RS layer 1, 2, 3 and 4 are corresponding to MIMO layer 1, 2, 3 and 4.
One of the key features of LTE is the possibility to transmit multicast or broadcast data from multiple cells over a synchronized single frequency network which is known as multimedia broadcast single frequency network (MBSFN) operation. In MBSFN operation, UE receives and combines synchronized signals from multiple cells. To facilitate this, UE needs to perform a separate channel estimation based on an MBSFN reference signal. In order to avoid mixing the MBSFN reference signal and normal reference signal in the same sub-frame, certain sub-frames known as MBSFN sub-frames are reserved from MBSFN transmission.
The structure of an MBSFN sub-frame is shown in FIG. 3 up to two of the first OFDM symbols are reserved for non-MBSFN transmission and the remaining OFDM symbols are used for MBSFN transmission. In the first up to two OFDM symbols, PDCCH for uplink resource assignments and PHICH can be transmitted and the cell-specific reference signal is the same as non-MBSFN transmission sub-frames. The particular pattern of MBSFN sub-frames in one cell is broadcasted in the system information of the cell. UEs not capable of receiving MBSFN will decode the first up to two OFDM symbols and ignore the remaining OFDM symbols. MBSFN sub-frame configuration supports both 10 ms and 40 ms periodicity. However, sub-frames with number 0, 4, 5 and 9 cannot be configured as MBSFN sub-frames. FIG. 3 illustrates the format of an MBSFN subframe. The PDCCH information sent on the L1/L2 control signaling may be separated into the shared control information and dedicated control information.
The frequency spectrum for IMT-advanced was decided at the World Radio Communication Conference (WRC-07) in November 2008. However, the actual available frequency bandwidth may differ for each region or country. The enhancement of LTE standardized by 3GPP is called LTE-advanced (LTE-A) and has been approved as the subject matter of Release 10. LTE-A Release 10 employs carrier aggregation according to which two or more component carriers as defined for LTE Release 8 are aggregated in order to support wider transmission bandwidth, for instance, transmission bandwidth up to 100 MHz. More details on carrier aggregation can be found in 3GPP TS 36.300 “Evolved Universal terrestrial Radio Access (E-UTRA) and Universal terrestrial Radio Access Network (E-UTRAN); Overall description”, v10.2.0, December 2010, Section 5.5 (Physical layer), Section 6.4 (Layer 2) and Section 7.5 (RRC), freely available at http://www.3gpp.org/ and incorporated herein by reference. It is commonly assumed that the single component carrier does not exceed a bandwidth of 20 MHz. A terminal may simultaneously receive and/or transmit on one or multiple component carriers depending on its capabilities. A UE may be configured to aggregate a different number of component carriers (CC) in the uplink and in the downlink. The number of downlink CCs which can be configured depends on the downlink aggregation capability of the UE. The number of uplink CCs which can be configured depends on the uplink aggregation capability of the UE. However, it is not possible to configure a UE with more uplink CCs than downlink CCs.
The term “component carrier” is sometimes replaces with the term “cell” since, similar to a concept of a cell known from earlier releases of LTE and UMTS, a component carrier defines resources for transmission/reception of data and may be added/reconfigures/removed from the resources utilized by the wireless nodes (e.g. UE, RN). In particular, a cell is a combination of downlink and optionally uplink resources, i.e. downlink and optional uplink component carrier. In Rel-8/9, there are one carrier frequency of downlink resources and one carrier frequency of uplink resources. The carrier frequency of downlink resources is detected by UE through cell selection procedure. The carrier frequency of uplink resources is informed to UE through System Information Block 2. When carrier aggregation is configured, there are more than one carrier frequency of downlink resources and possibly more than one carrier frequency of uplink resources. Therefore, there would be more than one combination of downlink and optionally uplink resources, i.e. more than one serving cell. The primary serving cell is called Primary Cell (PCell). Other serving cells are called Secondary Cells (SCells).
When carrier aggregation is configured, a UE has only one Radio Resource Control (RRC) connection with the network. Primary Cell (PCell) provides the non-access stratum (NAS) mobility information and security input at RRC connection reestablishment or handover. Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. RRC connection is the connection between RRC layer on UE side and RRC layer on network side. Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN include: allocation of temporary identifiers between UE and E-UTRAN; configuration of signaling radio bearer(s) for RRC connection, i.e, Low priority SRB and high priority SRB. More details on RRC can be found in 3GPP TS 36.331 “Evolved Universal terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification”, v10.0.0, December 2010, freely available at http://www.3gpp.org/ and incorporated herein by reference.
In the downlink, the carrier corresponding to PCell is called Downlink Primary Component Carrier (DL PCC) whereas in the uplink, the carrier corresponding to PCell is called Uplink Primary Component Carrier (UL PCC). The linking between DL PCC and UL PCC is indicated in the system information (System Information Block 2) from the PCell. System information is common control information broadcast by each cell, including, for instance, information about the cell to the terminals. With regard to the system information reception for the PCell, the procedure of LTE in Rel-8/9 applies. The details on system information reception procedure for Rel-8/9 can be found in 3GPP TS 36.331 “Evolved Universal terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification”, v9.5.0, December 2010, Section 5.2, freely available at http://www.3gpp.org/ and incorporated herein by reference. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC). The linking between DL SCC and UL SCC is indicated in the system information (System Information Block 2) of the SCell. All required system information of the SCell is transmitted to UE through dedicated RRC signaling when adding an SCell. Hence, there is no need for the UE to acquire system information directly from SCells. The system information of an SCell remains valid as long as the SCell is configured. Changes in system information of an SCell are handled through the removal and addition of the SCell. Removal and/or addition of an SCell can be performed using an RRC procedure.
Both downlink grant and uplink grant are received on DL CC. Therefore, in order to know the uplink grant received on one DL CC corresponds to the uplink transmission of which UL CC, the linking between DL CC and UL CC would be necessary.
A linking between UL CC and DL CC allows identifying the serving cell for which the grant applies:                downlink assignment received in PCell corresponds to downlink transmission in the PCell,        uplink grant received in PCell corresponds to uplink transmission in the PCell,        downlink assignment received in SCellN corresponds to downlink transmission in the SCellN,        uplink grant received in SCellN corresponds to uplink transmission in the SCellN. If SCellN is not configured for uplink usage by the UE, the grant is ignored by the UE.        
3GPP TS 36.212 v10.0.0, also describes in Section 5.3.3.1 the possibility of cross-carrier scheduling, using a Carrier Indication Field (CIF).
UE may be scheduled over multiple serving cells simultaneously. A cross-carrier scheduling with a CIF allows the PDCCH of a serving cell to schedule resources in another serving cell(s), however, with the following restrictions:                cross-carrier scheduling does not apply to PCell, which means that PCell is always scheduled via its own PDCCH,        when the PDCCH of a secondary cell (SCell) is configured, cross-carrier scheduling does not apply to this SCell, which means that the SCell is always scheduled via its own PDCCH, and        when the PDCCH of an SCell is not configured, cross-carrier scheduling applies and such SCell is always scheduled via PDCCH of another serving cell.        
Therefore, if there is no CIF, the linking between DL CC and UL CC identifies the UL CC for uplink transmission; if there is CIF, the CIF value identifies the UL CC for uplink transmission.
The set of PDCCH candidates to monitor, where monitoring implies attempting to decode each of the PDCCHs, are defined in terms of search spaces. A UE not configured with a Carrier Indicator Field (CIF) shall monitor one UE-specific search space at each of the aggregation levels 1, 2, 4, 8 on each activated serving cell. A UE configured with a Carrier Indicator Field (CIF) shall monitor one or more UE-specific search spaces at each of the aggregation levels 1, 2, 4, 8 on one or more activated serving cells. If a UE is configured with a CIF, the UE specific search space is determined by the component carrier, which means that the indices of CCEs corresponding to PDCCH candidates of the search space are determined by the Carrier Indicator Field (CIF) value. The carrier indicator field specifies an index of a component carrier.
If a UE is configured to monitor PDCCH candidates in a given serving cell with a given DCI format size with CIF, the UE shall assume that a PDCCH candidate with the given DCI format size may be transmitted in the given serving cell in any UE specific search space corresponding to any of the possible values of CIF for the given DCI format size. It means that if one given DCI format size can have more than one CIF value, UE shall monitor the PDCCH candidates in any UE specific search spaces corresponding to any possible CIF value with that given DCI format.
Further details on configurations of search spaces with and without CIF as defined in LTE-A for PDCCH can be found in 3GPP TS 36.213 “Evolved Universal terrestrial Radio Access (E-UTRA); Physical Layer procedures”, v10.0.0, December 2010, Section 9.1.1, freely available at http://www.3gpp.org/ and incorporated herein by reference.
Another key feature of the LTE-A is providing relaying functionality by means of introducing relay nodes to the UTRAN architecture of 3GPP LTE-A. Relaying is considered for LTE-A as a tool for improving the coverage of high data rates, group mobility, temporary network deployment, the cell edge throughput and/or to provide coverage in new areas.
A relay node is wirelessly connected to radio access network via a donor cell. Depending on the relaying strategy, a relay node may be part of the donor cell or, alternatively, may control the cells on its own. In case the relay node is a part of the donor cell, the relay node does not have a cell identity on its own, however, may still have a relay ID. In the case the relay node controls cells on its own, it controls one or several cells and a unique physical layer cell identity is provided in each of the cells controlled by the relay. At least, “type 1” relay nodes will be a part of 3GPP LTE-A. A “type 1” relay node is a relaying node characterized by the following:                The relay node controls cells each of which appears to a user equipment as a separate cell distinct from the donor cell.        The cells should have its own physical cell ID as defined in LTE Release 8 and the relay node shall transmit its own synchronization channels, reference symbols etc.        Regarding the single cell operation, the UE should receive scheduling information and HARQ feedback directly from the relay node and send its controlled information (acknowledgments, channel quality indications, scheduling requests) to the relay node.        The relay node should appear as a 3GPP LTE compliant eNodeB to 3GPP LTE compliant user equipment in order to support the backward compatibility.        The relay node should appear differently to the 3GPP LTE eNodeB in order to allow for further performance enhancements to the 3GPP LTE-A compliant user equipments.        
FIG. 4 illustrates an example 3GPP LTE-A network structure using relay nodes. A donor eNodeB (d-eNB) 410 directly serves a user equipment UE1 415 and a relay node (RN) 420 which further serves UE2 425. The link between donor eNodeB 410 and the relay node 420 is typically referred to as relay backhaul uplink/downlink. The link between the relay node 420 and user equipment 425 attached to the relay node (also denoted r-UEs) is called (relay) access link.
The donor eNodeB transmits L1/L2 control and data to the micro-user equipment UE1 415 and also to a relay node 420 which further transmits the L1/L2 control and data to the relay-user equipment UE2 425. The relay node may operate in a so-called time multiplexing mode, in which transmission and reception operation cannot be performed at the same time. In particular, if the link from eNodeB 410 to relay node 420 operates in the same frequency spectrum as the link from relay node 420 to UE2 425, due to the relay transmitter causing interference to its own receiver, simultaneous eNodeB-to-relay node and relay node-to-UE transmissions on the same frequency resources may not be possible unless sufficient isolation of the outgoing and incoming signals is provided. Thus, when relay node 420 transmits to donor eNodeB 410, it cannot, at the same time, receive from UEs 425 attached to the relay node. Similarly, when a relay node 420 receives data from donor eNodeB, it cannot transmit data to UEs 425 attached to the relay node. Thus, there is a sub-frame partitioning between relay backhaul link and relay access link.
Regarding the support of relay nodes, in 3GPP it has currently been agreed that:                Relay backhaul downlink sub-frames during which eNodeB to relay downlink backhaul transmission is configured, are semi-statically assigned.        Relay backhaul uplink sub-frames during which relay-to-eNodeB uplink backhaul transmission is configured are semi-statically assigned or implicitly derived by HARQ timing from relay backhaul downlink sub-frames.        In relay backhaul downlink sub-frames, a relay node will transmit to donor eNodeB and consequently r-UEs are not supposed to expect receiving any data from the relay node. In order to support backward compatibility for UEs that are not aware of their attachment to a relay node (such as Release 8 UEs for which a relay node appears to be a standard eNodeB), the relay node configures backhaul downlink sub-frames as MBSFN sub-frames.        
In the following, a network configuration as shown in FIG. 4 is assumed for exemplary purposes. The donor eNodeB transmits L1/L2 control and data to the macro-user equipment (UE1) and 410 also to the relay (relay node) 420, and the relay node 420 transmits L1/L2 control and data to the relay-user equipment (UE2) 425. Further assuming that the relay node operates in a time-duplexing mode, i.e. transmission and reception operation are not performed at the same time. Whenever the relay node is in “transmit” mode, UE2 needs to receive the L1/L2 control channel and physical downlink shared channel (PDSCH), while when the relay node is in “receive” mode, i.e. it is receiving L1/L2 control channel and PDSCH from the Node B, it cannot transmit to UE2 and therefore UE2 cannot receive any information from the relay node in such a sub-frame. In the case that the UE2 is not aware that it is attached to a relay node (for instance, a Release-8 UE), the relay node 420 has to behave as a normal (e-)NodeB. As will be understood by those skilled in the art, in a communication system without relay node any user equipment can always assume that at least the L1/L2 control signal is present in every sub-frame. In order to support such a user equipment in operation beneath a relay node, the relay node should therefore pretend such an expected behavior in all sub-frames.
As shown in FIGS. 2 and 3, each downlink sub-frame consists of two parts, control channel region and data region. FIG. 5 illustrates an example of configuring MBSFN frames on relay access link in situation, in which relay backhaul transmission takes place. Each subframe comprises a control data portion 510, 520 and a data portion 530, 540. The first OFDM symbols 720 in an MBSFN subframe are used by the relay node 420 to transmit control symbols to the r-UEs 425. In the remaining part of the sub-frame, the relay node may receive data 540 from the donor eNodeB 410. Thus, there cannot be any transmission from the relay node 420 to the r-UE 425 in the same sub-frame. The r-UE receives the first up to two OFDM control symbols and ignores the remaining part of the sub-frame. Non-MBSFN sub-frames are transmitted from the relay node 420 to the r-UE 525 and the control symbols 510 as well as the data symbols 530 are processed by the r-UE 425. An MBSFN sub-frame can be configured for every 10 ms on every 40 ms. Thus, the relay backhaul downlink sub-frames also support both 10 ms and 40 ms configurations. Similarly to the MBSFN sub-frame configuration, the relay backhaul downlink sub-frames cannot be configured at sub-frames with #0, #4, #5 and #9. Those subframes that are not allowed to be configured as backhaul DL subframes are called “illegal DL subframes”. Thus, relay DL backhaul subframes can be normal or MBSFN subframe on d-eNB side. Currently it is agreed that relay backhaul DL subframes, during which eNB 410 to relay node 420 downlink backhaul transmission may occur, are semi-statically assigned. Relay backhaul UL subframes, during which relay node 420 to eNB 410 uplink backhaul transmission may occur, are semi-statically assigned or implicitly derived by HARQ timing from relay backhaul DL subframes.
Since MBSFN sub-frames are configured at relay nodes as downlink backhaul downlink sub-frames, the relay node cannot receive PDCCH from the donor eNodeB. Therefore, a new physical control channel (R-PDCCH) is used to dynamically or “semi-persistently” assign resources within the semi-statically assigned sub-frames for the downlink and uplink backhaul data. The downlink backhaul data is transmitted on a new physical data channel (R-PDSCH) and the uplink backhaul data is transmitted on a new physical data channel (R-PUSCH). The R-PDCCH(s) for the relay node is/are mapped to an R-PDCCH region within the PDSCH region of the sub-frame. The relay node expects to receive R-PDCCH within the region of the sub-frame. In time domain, the R-PDCCH region spans the configured downlink backhaul sub-frames. In frequency domain, the R-PDCCH region exists on certain resource blocks preconfigured for the relay node by higher layer signaling. Regarding the design and use of an R-PDCCH region within a sub-frame, the following characteristics have been agreed in standardization:                R-PDCCH is assigned PRBs for transmission semi-statically. Moreover, the set of resources to be currently used for R-PDCCH transmission within the above semi-statically assigned PRBs may vary dynamically, between sub-frames.        The dynamically configurable resources may cover the full set of OFDM symbols available for the backhaul link or may be constrained to their sub-set.        The resources that are not used for R-PDCCH within the semi-statically assigned PRBs may be used to carry R-PDSCH or PDSCH.        In case of MBSFN sub-frames, the relay node transmits control signals to the r-UEs. Then, it can become necessary to switch transmitting to receiving mode so that the relay node may receive data transmitted by the donor eNodeB within the same sub-frame. In addition to this gap, the propagation delay for the signal between the donor eNodeB and the relay node has to be taken into account. Thus, the R-PDCCH is first transmitted starting from an OFDM symbol which, within the sub-frame, is late enough in order for a relay node to receive it.        The mapping of R-PDCCH on the physical resources may be performed either in a frequency distributed manner or in a frequency localised manner.        The interleaving of R-PDCCH within the limited number of PRBs can achieve diversity gain and, at the same time, limit the number of PRBs wasted.        In non-MBSFN sub-frames, Release 10 DM-RS is used when DM-RS are configured by ENodeB. Otherwise, Release 8 CRS are used. In MBSFN sub-frames, Release 10 DM-RS are used.        R-PDCCH can be used for assigning downlink grant or uplink grant for the backhaul link. The boundary of downlink grant search space and uplink grant search space is a slot boundary of the sub-frame. In particular, the downlink grant is only transmitted in the first slot and the uplink grant is only transmitted in the second slot of the sub-frame.        No interleaving is applied when demodulating with DM-RS. When demodulating with CRS, both REG level interleaving and no interleaving are supported.        
Relay backhaul R-PDCCH search space is a region where relay node 420 expects to receive R-PDCCHs. In time domain, it exists on the configured DL backhaul subframes. In frequency domain, it exists on certain resource blocks that are configured for relay node 420 by higher layer signaling. R-PDCCH can be used for assigning DL grant or UL grant for the backhaul link.
According to agreements reached in RAN1 about the characteristics of the relay backhaul R-PDCCH in no cross-interleaving case, a UE-specific search space has following properties:                Each R-PDCCH candidate contains continuous VRBs,        The set of VRBs is configured by higher layers using resource allocation types 0, 1, or 2,        The same set of VRBs is configured for a potential R-PDCCH in the first and in the second slot,        DL grant is only received in 1st slot and UL grant is only received in 2nd slot, and        The number of candidates for the respective aggregation level {1, 2, 4, 8} is {6, 6, 2, 2}.        
R-PDCCH without cross-interleaving means that, an R-PDCCH can be transmitted on one or several PRBs without being cross-interleaved with other R-PDCCHs in a given PRB. In the frequency domain, the set of VRBs is configured by higher layer using resource allocation types 0, 1, or 2 according to Section 7.1.6 of 3GPP TS 36.213 “Evolved Universal terrestrial Radio Access (E-UTRA); Physical layer procedures”, v8.8.0, September 2009, freely available at http://www.3gpp.org/ and incorporated herein by reference. If the set of VRBs is configured by resource allocation type 2 with distributed VRB to PRB mapping, the provisions in Section 6.2.3.2 of 3GPP TS 36.211 for even slot numbers are always applied. The details can be found in 3GPP TS 36.211, “Evolved universal terrestrial radio access (E-UTRA); physical channels and modulations (Release 8)”, version 8.9.0, December 2009, Section 6.2, available at http://www.3gpp.org. which is incorporated herein by reference.
FIG. 6 shows the example of R-PDCCH downlink and uplink grant search space for the no cross-interleaved R-PDCCH case. In this example, no carrier aggregation and no cross-carrier scheduling is assumed. In the example, the same VRBs are configured for DL and UL grant search space. DL grant search space is only in the 1st slot and UL grant search space is only in 2nd slot. In particular, FIG. 6 shows schematically a first slot 610 and a second slot 620 in which the rows represent pairs of virtual resource blocks on different sub-carriers (i.e., in the frequency domain). Ellipses of different sizes represent candidates of the respective uplink and the downlink grant search space for different aggregation levels. For instance, the aggregation level 1 candidates 601 cover one VRB, candidates of aggregation level 2, 602, cover 2 VRBs, candidates of aggregation level 4, 604, cover 4 VRB and candidates of aggregation level 8, 608, cover 8 VRBs.
According to agreements reached in RAN1 regarding the R-PDCCH/R-PDSCH multiplexing, the second slot of an R-PDCCH PRB pair can be allocated to data channel for a relay node receiving at least a part of DL grant in the first slot of the PRB pair. In particular, when the relay node receives a resource allocation which overlaps a PRB pair, in which a DL grant is detected in the first slot, the relay node assumes that there is a PDSCH data transmission for it in the second slot of that PRB pair. Otherwise, the relay node assumes that there is no data transmission for it in the second slot of that PRB pair and thus also no change to DCI formats. For an R-PDCCH PRB pair where the relay node detects at least a part of DL grant in the first slot, the relay node shall assume the first slot of the R-PDCCH PRB pair is not used for data transmission.
Based on the above rules, FIG. 7 illustrates various allocation scenarios. In particular, FIG. 7 shows in its part (a) a smaller portion of the downlink and uplink grant search space as also illustrated in FIG. 6. In its parts (b), (c) and (d), FIG. 7 shows examples of the PRB utilization in different downlink and uplink grant allocation cases. In these examples, downlink and uplink grant is assumed to use aggregation level 2 candidates. In the first allocation example (b), only a downlink grant 702 is allocated, thus the second slot can be used for PDSCH 720. In the second allocation example (c), only uplink grant 703 is allocated, thus the corresponding PRBs 730 in the first slot are wasted. In the third allocation example (d), both downlink 741 and uplink 742 grants are allocated, so that they can be allocated in the same PRB pair, and thus no PRBs are wasted.
If carrier aggregation is supported on relay backhaul link, R-PDCCH search space should also be able to support carrier aggregation. In case of no cross-carrier scheduling, there is R-PDCCH region in each Component Carrier (CC). Accordingly, the R-PDCCH search space design applied in a case without carrier aggregation can be reused. However, in case of cross-carrier scheduling, there will be more than one R-PDCCH DL and/or UL grant search spaces in one CC, so that the R-PDCCH search space design cannot be easily reused.